if it does stop, what are the chances it ever goes to the Supreme Court for a decision that will define personal privacy in the face of these newly wide-spread invasive technologies?
Not terrible. A person whose constitutional rights have been violated can sue under USC ยง1983 for damages. They would almost certainly lose, but the court making the decision would still need to decide the constitutionality of the underlying act. So even if the TSA stopped, assuming someone had already been treated to particularly egregious conduct, the case might still go to the courts.
Even without that, though, we can cobble together existing supreme court decisions to know with a good deal of certainty what can or cannot be done. First, both x-raying and physically searching people are "searches," so the 4th amendment applies to them. Because they're searches, the government has to come up with a reason to do them. The government can't rely on probable cause or reasonable suspicion to justify the search because everyone goes through it, so it will have to rely on "special needs."
The "special needs" category of searches justifies searches that are for purposes other than catching criminals (in this case, public safety would be that purpose though of course criminals would be caught as a result). Such searches can be conducted without suspicion of the target or consent of the target, but they must be limited in scope to what is necessary in order for them to be effective, and police must have little or no discretion as to who is targeted, so not "anyone in this line of people I feel like" but "every fifth person followed by every third person, no exceptions." The supreme court has approved airport metal detector searches for weapons as valid, so the big question there is, are these new searches no more invasive than is necessary for them to be effective?
EDIT: also,
thisEDIT 2: removed the "consent" stuff because airport searches for weapons are indeed special needs searches.
